Thank you all for your advice! We were not very impressed in general, but then we didn't arrive on the right time for most restaurants mentioned, and one of the restaurants gave me food poisoining so there was little opportunity left to eat.
We did buy great oysters and fresh mussels in the Fish on the Quay next to the Harbourmaster in Aberaeron.
At The Ship in Tresaith we had the best English Breakfast of our lives. I didn't know every single component can have so much distinct taste on its own, from tomato to sausage to mushroom to egg. Sadly we were too early for lunch, but the menu looked delicious and the service was very friendly.
We also had a decent dinner at the Cwtch in St Davids, with ups (the bread and the soup), downs (the non-tender porc belly) and unexciting standards (fishcakes, steak, potato gratin).
The ales were good, and I look forward to visiting the North one day for more discoveries! Thank you again for your advice!
I do hope that you are heading West before heading North. Newport in Pembrokeshire (between Fishguard and Cardigan,) offers several options especially Cnapan and also Llys Meddig. (Cnapan also has rooms.) There is a very good cheesemaker near Cenarth called Caws (Caws = cheese) Cenarth. Sewin (fish) is another local speciality to be tried. If you are into ales, try the microbrewery at the Nag's Head in Abercych. Delish!
Slightly further north, over the border into Ceredigion, head to Tresaith beach to The Ship for home-cooked food.
Then as Harters says, Aberaeron is definitely a good idea. The Harbourmaster is excellent, and has been ahead of the competition for years, and is still deservedly thus regarded. I can't think of anything positive to say about Aberystwyth at all, and holding up my hands being of Cardi stock, things only get worse north of Machynlleth. If you're heading up there, at least master Diolch (thank you).
well Diolch very much! This also helps us plan the trip: the plan now is to go up till Aberaeron for one day (we're invited to stay one night in Lampeter) and then to go down west and explore the coast and the fish. Unfortunately no time to go further north to Harlech.
I have some dental issues right now and can't wait to embark on a diet of fish and cheese! (and ales...) Am heading to Swansea tomorrow and very excited.
Maes-y-Neuadd country house restaurant is only a mile from the A496 coastal road as it heads inland north of Harlech. I've had several decent meals there and given the quality of the cooking and the standard of produce, I reckon it offers excellent value for money.
The rooms are pleasant enough, but as is normal with a country house with a decent restaurant, they're a tad overpriced.
Sample winter menu available halfway down this page ... http://www.neuadd.com/restaurant.htm
ETA: Seems PhilD didn't have as good an experience there - and his complaint about the wine service is valid (http://chowhound.chow.com/topics/4563...). So your mileage may vary.